Common waveguide circulators have metal waveguide arms that meet in a common junction region having a ferrite element. Dielectric transformers are employed in the circulators to provide an impedance match between the waveguides, which are typically air-filled, and the ferrite element. When a magnetizing field is created in this ferrite element, a gyromagnetic effect is produced that can be used for circulating a microwave signal from one waveguide arm to another. By reversing the direction of the magnetizing field, the direction of circulation between the waveguide arms is reversed. These waveguide circulators can be connected in various configurations to produce waveguide switching networks.
Conventional waveguide circulator switching networks that include multiple ferrite elements typically have impedance-matching transitions and an air-filled waveguide section between the ferrite elements. For example, standard waveguide circulators may transition from one ferrite element to a one-quarter wavelength dielectric transformer, to an air-filled waveguide section, and then to another one-quarter wavelength dielectric transformer, and the next ferrite element. The dielectric transformers are typically used to match the lower impedance of the ferrite element to that of the air-filled waveguide.
The air-filled waveguide section between dielectric transformers is sufficiently long, generally at least a quarter-wavelength, to allow the fields to transition back to the standard waveguide mode between circulators. Thus, the conventional transition between ferrite elements occurs over a length of three-quarters of a wavelength or greater between adjacent ferrite elements. This sets the minimum separation distance that can be obtained in multi-junction assemblies when input/output ports of multiple circulators are intercoupled to provide a more complex microwave switching or isolation arrangement. This can result in a multi-junction waveguide structure that is undesirably large and heavy. Furthermore, the insertion loss of a multiple circulator assembly increases as the separation distance between ferrite elements is increased as a result of the finite conductivity of the waveguide structure.